The Treasury Department sold $6.4 billion of new three-month bills and $6.4 billion of new six-month bills at the identical discount rate of 5.55%. Three- and six-month bills went at an identical 5.58% last week. The rates were the lowest since March 2, when three-month bills averaged 5.47% and six-month bills sold for 5.51%. The new discount rates understate the actual return to investors--5.72% for three-month bills, with a $10,000 bill selling for $9,859.70, and 5.81% for six-month bills selling for $9,719.40. The discount rate reflects the price discount received when government securities are purchased at less than face value.